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ASN Wikibase Occurrence # 137259
Last updated: 21 September 2021
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Time:19:17 LT
Type:Silhouette image of generic AS50 model; specific model in this crash may look slightly different
Eurocopter AS 350B3 Ecureuil
Owner/operator:Blueway Helicopter AS/Airlift AS
Registration: LN-OXC
MSN: 4260
Fatalities:Fatalities: 5 / Occupants: 5
Other fatalities:0
Aircraft damage: Written off (damaged beyond repair)
Location:Ullensvang, Hardanger, Hordaland -   Norway
Phase: En route
Departure airport:Kinsarvik
Destination airport:Kinsarvik
The helicopter was used to transport people to a cabin site in the mountains. The weather was good with fine flying conditions. The first flight with five passengers had been completed. There were four passengers on board during the second flight. As the helicopter started the descent towards the cabin site, the passengers of the first flight witnessed the helicopter turning tightly to the right. The witnesses have explained that during the turn, control of the helicopter appeared to be lost with an estimated bank angle of 60-90 degrees in a steep descent. At the end, it seemed as if control was about to be regained, but the helicopter hit the ground hard about 500 metres short of the planned landing site and immediately caught fire. All five persons on board were fatally injured. The helicopter was a total loss.
The forward speed at ground impact has been calculated to about 105 kt (194 km/h) based on tracks at the accident site. The helicopter hit the ground with a nearly flat pitch angle and about 45° of bank to the right. The investigation has not revealed any technical defects or irregularities that could have influenced the course of events. The extensive fire damage made parts of the helicopter unavailable for examination, but it was possible to establish that the engine was delivering power to the rotors when the accident happened. It was also possible to verify that key parts of the flight controls were intact prior to ground impact.
The AIBN considers it likely that abrupt manoeuvring initiated a sequence where control of the helicopter was partly lost for a period, and that the height was insufficient for the commander to recover in time.
The AIBN believes that the hydraulic system may have reached its limitation during the manoeuvring, resulting in the phenomenon servo transparency, (also called jack stall) occurring. When this phenomenon occurs in a right turn, it can cause the helicopter to deviate substantially from the intended flight path and simultaneously counter the pilot's efforts to recover. The AIBN believes that warnings about this hazard should be made clearer in the Rotorcraft Flight Manual. This type of helicopter has no warning light or other means to provide warning of imminent servo overload. In addition to high mass, high speed and high torque, high density altitude (‘thin air’) are among the factors that precipitate overload. This means that servo transparency will occur more easily when flying a heavily loaded helicopter in the mountains on a hot day, as the case was with LN-OXC.
It is not possible to conclude with certainty what flight attitudes and loads the helicopter was subjected to, which airspeed it held and the flight path it followed in the turn preceding the crash. Current regulations do not require use of flight recorders in light aircraft. The Accident Investigation Board believes that the time has come to utilise available, light flight recorders to provide a better data basis for accident investigations and other safety enhancing activities. This is one of 8 accidents that resulted in an EASA rule making team on in-flight recording for light aircraft.

Sources: (photo)

Revision history:

04-Jul-2011 13:53 whiteshark Added
04-Jul-2011 14:34 RobertMB Updated [Time, Aircraft type, Operator, Phase, Source, Narrative]
05-Jul-2011 02:47 Anon. Updated [Aircraft type]
05-Jul-2011 03:03 whiteshark Updated [Registration, Location, Departure airport, Destination airport, Narrative]
05-Jul-2011 03:11 RobertMB Updated [Aircraft type, Registration, Source]
07-Jul-2011 06:43 Anon. Updated [Narrative]
08-Jul-2011 07:06 RobertMB Updated [Registration, Cn, Operator, Source]
08-Jul-2011 07:09 RobertMB Updated [Operator]
07-Nov-2012 11:58 harro Updated [Source, Narrative]
02-Aug-2014 14:08 Aerossurance Updated [Source]
03-Aug-2014 07:24 Aerossurance Updated [Source, Narrative]
05-Sep-2017 17:16 TB Updated [Operator, Location, Narrative]

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